Ribbon bonding tools, and methods of designing ribbon bonding tools

ABSTRACT

A ribbon bonding tool is provided. The ribbon bonding tool includes a body portion including a tip portion, the tip portion defining a working surface. The ribbon bonding tool includes a group of four protrusions extending from the working surface, wherein the working surface defines four quadrants in a horizontal plane by extending an imaginary line at a midpoint along each of a length and a width of the working surface. Each of the four protrusions is arranged in one of four quadrants.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.15/338,948, filed Oct. 31, 2016, which claims the benefit of U.S.Provisional Application No. 62/250,694, filed Nov. 4, 2015, the contentsof which are incorporated herein by reference.

FIELD

The invention relates to the ultrasonic bonding, and more particularly,to improved bonding tools for bonding conductive wire and ribbonmaterial.

BACKGROUND

In the semiconductor packaging industry, and other industries requiringelectrical interconnection, wire and ribbon bonding are widely adoptedtechnologies. In connection with wire and ribbon bonding operations,various types of energy (e.g., ultrasonic energy, thermosonic energy,thermocompressive energy, etc.) are used to bond an end portion ofwire/ribbon to a first bonding location. After a first bond is formed atthe first bonding location, a length of wire/ribbon is extended tosecond bonding location, and then a second bond is formed at the secondbonding location.

As opposed to conventional wire bonding (e.g., ball bonding and wedgebonding of a wire having a round cross section), ribbon bondingtypically involves bonding a flexible conductive ribbon material (e.g.,having a rectangular cross section) between bonding locations. Exemplaryconductive materials used in ribbon bonding include aluminum (Al) ribbonmaterial, copper (Cu) ribbon material, aluminum copper clad ribbonmaterial (Al—Cu), amongst others. Exemplary ribbon bonding techniques,and packages including conductive ribbon, are disclosed in U.S. Pat.Nos. 7,745,253, 8,685,789, and 8,685,791. Exemplary ribbon bonding toolsare disclosed in U.S. Pat. Nos. 7,838,101 and 8,820,609.

A challenge in ribbon bonding is extending the usable life (e.g., innumber of bonds) of a ribbon bonding tool. Extending the useful life ofthe tool is particularly challenging in applications involving Cu ribbonmaterial, Al—Cu ribbon material, etc.

Thus, it would be desirable to provide improved ribbon bonding tools,and methods of designing ribbon bonding tools.

SUMMARY

According to an exemplary embodiment of the invention, a ribbon bondingtool is provided. The ribbon bonding tool includes a body portionincluding a tip portion, the tip portion defining a working surface. Theribbon bonding tool includes a group of four protrusions extending fromthe working surface, wherein the working surface defines four quadrants(e.g., see Quadrants 1, 2, 3, and 4 in FIG. 2C) in a horizontal plane byextending an imaginary line at a midpoint along each of a length and awidth of the working surface (e.g., see imaginary “Length line” at themidpoint of the length, and imaginary “Width line” at the midpoint ofthe width, in FIG. 2C). Each of the four protrusions is arranged in oneof four quadrants (or each of the four protrusions being at leastpartially in a respective one of the four quadrants).

According to another exemplary embodiment of the invention, a ribbonbonding tool is provided. The ribbon bonding tool includes a bodyportion including a tip portion, the tip portion defining a workingsurface. The ribbon bonding tool includes a group of four protrusionsextending from the working surface. Each of the four protrusions arearranged equidistant (or substantially equidistant) from a center point(e.g., see center point in FIG. 2C) of the working surface.

According to another exemplary embodiment of the invention, a method ofdesigning a ribbon bonding tool is provided. The method includes: (a)determining locations for each of four protrusions on a working surfaceof the ribbon bonding tool such that the four protrusions will havesubstantially similar wear characteristics over a predetermined periodof time; (b) determining shapes for each of the four protrusions suchthat each of the four protrusions will have a substantially similar wearcharacteristic along its specific length over the predetermined periodof time; and (c) forming the ribbon bonding tool to have shapes of thefour protrusions determined in step (b) at the locations determined instep (a).

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed descriptionwhen read in connection with the accompanying drawings. It is emphasizedthat, according to common practice, the various features of the drawingsare not to scale. On the contrary, the dimensions of the variousfeatures are arbitrarily expanded or reduced for clarity. Included inthe drawings are the following figures:

FIGS. 1A-1B are front and side view diagrams of a ribbon bonding tool inaccordance with an exemplary embodiment of the invention;

FIGS. 2A-2E are various views of a tip portion of a ribbon bonding toolin accordance with an exemplary embodiment of the invention;

FIGS. 3A-3E are various views of a tip portion of another ribbon bondingtool in accordance with an exemplary embodiment of the invention;

FIGS. 4A-4E are various views of a tip portion of yet another ribbonbonding tool in accordance with an exemplary embodiment of theinvention;

FIGS. 5A-5E are various views of a tip portion of yet another ribbonbonding tool in accordance with an exemplary embodiment of theinvention;

FIGS. 6A-6E are various views of a tip portion of yet another ribbonbonding tool in accordance with an exemplary embodiment of theinvention; and

FIG. 7 is a flow diagram illustrating a method of designing a ribbonbonding tool in accordance with an exemplary embodiment of theinvention.

DETAILED DESCRIPTION

A factor contributing to the reduced lifetime of certain ribbon bondingtools is the uneven wear across the bond foot (including the workingsurface) of the ribbon bonding tool. In accordance with certainexemplary embodiments of the invention, ribbon bonding tools areprovided including protrusions/structures at locations on the workingsurface (i.e., extending from a working surface of the bonding tool)where the wear rate is similar, and to avoid havingprotrusions/structures at certain locations on the bond foot (e.g., thecenter of the working surface).

Such ribbon bonding tools may have a substantially increased usablelifetime (e.g., measured in number of bonds)—wherein during the useablelifetime the geometry of the contact portion of the bonding tool (theportion that contacts the ribbon material during bonding) remains withina specific range of the geometry at time zero (i.e., at a time when zerobonds have been formed with the ribbon bonding tool). During the useablelifetime, the bond process behavior and result remain within a specificwindow, with deviations from the results at time zero less than apredetermined tolerance.

As provided above, the protrusions/structures on the working surface maydesirably be arranged at locations where they encounter similar wearrates. Certain locations (e.g., unique locations, such as thecenter/midpoint of the working surface) have no such protrusion. Theprotrusions/structures are shaped such that the local wear rate acrossthe protrusions/structures themselves is within a predeterminedtolerance of one another, such that the protrusions do not change theirshape significantly during their usable lifetime.

FIGS. 1A-1B are front and side views of a ribbon bonding tool 100 (FIG.1A illustrates a front 100 c of a body portion of ribbon bonding tool100, and FIG. 1B illustrates a side 100 d of the body portion of ribbonbonding tool 100). At an end of the body portion of ribbon bonding tool100 is tip portion 100 b. Tip portion 100 b defines a working surface100 a. A group of four protrusions 102 a extend from working surface 100a.

FIGS. 2A-2E, 3A-3E, 4A-4E, 5A-5E, and 6A-6E are examples of ribbonbonding tools 100. That is, each of FIGS. 2A-2E, 3A-3E, 4A-4E, 5A-5E,and 6A-6E illustrate a respective tip portion 100 b (i.e., 100 b 1, 100b 2, 100 b 3, 100 b 4, and 100 b 5).

FIG. 2A is a perspective view of a tip portion 100 b 1 defining aworking surface 100 al. Four elongate protrusions 102 a 1 extend fromworking surface 100 al. FIG. 2B is a top perspective view of tip portion100 b 1; FIG. 2C is a top view of tip portion 100 b 1; FIG. 2D isanother top perspective view of tip portion 100 b 1; and FIG. 2E is atop view illustration of protrusions 102 a 1. Areas 102 b 1 of workingsurface 100 a 1 away from protrusions 102 a 1 (e.g., between and/oraround protrusions 102 a 1) are substantially planar. Each of the fourprotrusions 102 a 1 includes two side wall portions extending along alength of the protrusions, each of the two side wall portions followinga substantially straight linear path. In FIGS. 2A-2E, each of the fourprotrusions 102 a 1 has an elongate structure extending between ends 102a 1 c, and a substantially planar contact surface 102 a 1 a. Each of thefour protrusions 102 a 1 includes tapered wall portions 102 a 1 bextending along a height of the protrusions 102 a 1.

Tip portion 100 b 2 (defining a working surface 100 a 2) in FIGS. 3A-3E,and the views of tip portion 100 b 2, are very similar to tip portion100 b 1 in FIGS. 2A-2E. Referring to FIGS. 3A-3E, areas 102 b 2 ofworking surface 100 a 2 away from elongate protrusions 102 a 2 aresubstantially planar. Each of the four protrusions 102 a 2 (having anelongate structure extending between ends 102 a 2 c, and including asubstantially planar contact surface 102 a 2 a) includes one side wallportion following a substantially straight linear path, and another sidewall portion following a curved path. Protrusions 102 a 2 includetapered wall portions 102 a 2 b extending along a height of theprotrusions 102 a 2.

Tip portion 100 b 3 (defining a working surface 100 a 3) in FIGS. 4A-4E,and the views of tip portion 100 b 3, are very similar to tip portion100 b 1 in FIGS. 2A-2E. Referring to FIGS. 4A-4E, areas 102 b 3 ofworking surface 100 a 3 away from elongate protrusions 102 a 3 aresubstantially planar. Each of the four protrusions 102 a 3 (having anelongate structure extending between ends 102 a 3 c, and including asubstantially planar contact surface 102 a 3 a) includes two side wallportions following a curved path. Protrusions 102 a 3 include taperedwall portions 102 a 3 b extending along a height of the protrusions 102a 3.

Tip portion 100 b 4 (defining a working surface 100 a 4) in FIGS. 5A-5E,and the views of tip portion 100 b 4, are very similar to tip portion100 b 1 in FIGS. 2A-2E. Referring to FIGS. 5A-5E, areas 102 b 4 ofworking surface 100 a 4 away from elongate protrusions 102 a 4 aresubstantially planar. Each of the four protrusions 102 a 4 (having anelongate structure extending between ends 102 a 4 c, and including asubstantially planar contact surface 102 a 4 a) includes one side wallportion following a substantially straight linear path, and another sidewall portion following a curved path. Protrusions 102 a 4 includetapered wall portions 102 a 4 b extending along a height of theprotrusions 102 a 4.

Tip portion 100 b 5 (defining a working surface 100 a 5) in FIGS. 6A-6E,and the views of tip portion 100 b 5, are very similar to tip portion100 b 1 in FIGS. 2A-2E. Referring to FIGS. 6A-6E, areas 102 b 5 ofworking surface 100 a 5 away from elongate protrusions 102 a 5 aresubstantially planar. Each of the four protrusions 102 a 5 (having anelongate structure extending between ends 102 a 5 c, and including asubstantially planar contact surface 102 a 5 a) includes one side wallportion following a substantially straight linear path, and another sidewall portion following a non-linear path. Protrusions 102 a 5 includetapered wall portions 102 a 5 b extending along a height of theprotrusions 102 a 5.

FIG. 7 is a flow diagram in accordance with certain exemplaryembodiments of the invention. As is understood by those skilled in theart, certain steps included in the flow diagram may be omitted; certainadditional steps may be added; and the order of the steps may be alteredfrom the order illustrated.

FIG. 7 is a flow diagram illustrating a method of designing a ribbonbonding tool in accordance with an exemplary embodiment of theinvention. At Step 700, locations for each of four protrusions on aworking surface of the ribbon bonding tool are determined such that thefour protrusions will have similar (or substantially similar) wearcharacteristics over a predetermined period of time (e.g., the useablelifetime of the ribbon bonding tool). For example, experimentation maybe done in connection with the application (e.g., a specific ribbonmaterial, a specific bonding machine, specific bond process parameters,etc.) to determine how the bond foot of the ribbon bonding tool willwear. Through continued experimentation, desired locations for theprotrusions can be determined. At Step 702, shapes for each of the fourprotrusions are determined such that each of the four protrusions willhave a similar (or substantially similar) wear characteristic along itsspecific length over the predetermined period of time (e.g., the useablelifetime of the ribbon bonding tool). For example, shapes of theprotrusions may be altered during experimentation to find shapes havingsimilar (or substantially similar) wear characteristics along itslength. At Step 704, the ribbon bonding tool is formed to have shapes ofthe four protrusions determined in Step 702 at the locations determinedin Step 700. For example, a tip portion of a ribbon bonding tool formedfrom a unitary piece of material (e.g., a metal such as steel, tungstencarbide, a ceramic tip portion attached to a metal (e.g., tungstencarbide) body portion of the ribbon bonding tool, etc.) may be machinedto form the desired shapes of the protrusions (e.g., using a processsuch as laser machining, electrical discharge machining, sinker EDM,etc.). Although the method illustrated in FIG. 7 has been described inconnection with four protrusions (e.g., one protrusion in each quadrant,as described above), the steps shown in FIG. 7 may be used to design aribbon bonding tool having more (or less) than four protrusions.

In accordance with certain exemplary embodiments of the invention,because of the substantially uniform wear of the four protrusions withrespect to one another, and the substantially uniform wear across thearea of each of the protrusions, the actual wear during the lifetime ofthe tool tends to not affect performance of the tool. This tends to bethe case particularly if the sidewalls are substantially vertical,because the contact area does not significantly change during thelifetime of the tool.

As will be appreciated by those skilled in the art, the wear behavior ofribbon bonding tools may change significantly once the ribbon materialcomes into contact with the working surface (i.e., the horizontal plane)of the ribbon bonding tool. Thus, it would be desirable to predict thetime when the ribbon material comes into contact with the workingsurface of the ribbon bonding tool. For example, certain signals may bemonitored on a wire/ribbon bonding machine that provide an indication (asignature) of contact between the ribbon material and the workingsurface of the ribbon bonding tool. Upon detection of such anindication, a user of the machine may replace the ribbon bonding tool.

One signal that may be monitored to predict such an indication is ribbonmaterial deformation. That is, when the protrusions/structures wear, theprotrusions/structures penetrate the ribbon material to a lesser degree.The deformation caused by this reduced penetration can be measured(e.g., using a z-axis detection system associated with the bond headposition of the wire/ribbon bonding machine).

Another option would be to include a feature on the working surface(e.g., in the center of the working surface) that, upon a certain amountof wear of the protrusions, results in an additional mark to becomevisible (e.g., the mark may become visible on the ribbon material beingbonded) such that the user knows that it is time to replace the ribbonbonding tool. The mark may be detected, for example, using a camera ofthe wire/ribbon bonding machine. The imaging by the camera may beperformed on a predetermined interval (e.g., after every thousandbonding cycles, etc.).

Bonding tools according to the invention may be formed from a singlepiece of material (e.g., where the body portion, including the tipportion, and including the protrusions on the tip portion, may be formedfrom a single piece of material). Bonding tools according to theinvention may also be formed from two or more pieces (e.g., a tipportion formed of a piece of material coupled to a separate bodyportion). Further still, the protrusions described herein may be formedfrom the same piece of material as the remainder of the tip portion, ormay be separates pieces of material attached to the working face of thetip portion. Additional implementations, within the scope of theinvention, are contemplated.

Although the invention has been described primarily with respect toribbon bonding tools it is not limited thereto. For example, theteachings of the invention may have applicability to other wire bondingtools (e.g., wedge bonding tools, ball bonding tools, etc.). Further,additional or different numbers of protrusions (e.g., a plurality ofprotrusions other than four) may be provided on the working surface ofthe ribbon bonding tool.

Although the invention is illustrated and described herein withreference to specific embodiments, the invention is not intended to belimited to the details shown. Rather, various modifications may be madein the details within the scope and range of equivalents of the claimsand without departing from the invention.

What is claimed:
 1. A ribbon bonding tool comprising: a body portionincluding a tip portion, the tip portion defining a working surface, theworking surface being longer along a length direction of the workingsurface as compared to a width direction of the working surface, in afirst direction the tip portion being configured to bond a portion of aribbon material to a bonding location; and a group of four protrusionsextending from the working surface, wherein the working surface definesfour quadrants in a horizontal plane by extending an imaginary line at amidpoint along each of a length and a width of the working surface, eachof the four protrusions being arranged in one of four quadrants, whereineach of the four protrusions has an elongate structure with asubstantially planar contact surface, wherein the substantially planarcontact surface is longer along the length direction as compared to thewidth direction, and wherein each of the four protrusions includestapered wall portions extending along a height thereof.
 2. The ribbonbonding tool of claim 1 wherein the body portion and the fourprotrusions are formed from a single piece of material.
 3. The ribbonbonding tool of claim 1 wherein a center point of the working surface issubstantially planar.
 4. The ribbon bonding tool of claim 1 wherein eachof the four protrusions are arranged equidistant from a center point ofthe working surface.
 5. A ribbon bonding tool comprising: a body portionincluding a tip portion, the tip portion defining a working surface, theworking surface being longer along a length direction of the workingsurface as compared to a width direction of the working surface, in afirst direction the tip portion being configured to bond a portion of aribbon material to a bonding location; and a group of four protrusionsextending from the working surface, wherein each of the four protrusionsare arranged equidistant from a center point of the working surface,wherein each of the four protrusions has an elongate structure with asubstantially planar contact surface, wherein the substantially planarcontact surface is longer along the length direction as compared to thewidth direction, and wherein each of the four protrusions includestapered wall portions extending along a height thereof.
 6. The ribbonbonding tool of claim 5 wherein the body portion and the fourprotrusions are formed from a single piece of material.